Electrically controlled micro-mirrors (most often using electrostatic, electromagnetic, piezoelectric, or thermoelastic forces) capable of generating digital or analog angular positions are known in the literature. They generally use hinge configurations making it possible, according to the complexity of the technological steps employed, to oscillate around an axis (simple hinge) or around two axes (double hinge) of rotation oriented most frequently orthogonally.
FIG. 1a represents a view of such an electrostatically controlled micro-mirror enabling rotation on 2 perpendicular axes, utilized in optical routing systems. The fixed frame 2 of the micro-mirror and the movable parts 3 and 4 articulated, respectively, around hinges 5 and 6 that enable the desired rotations about the two orthogonal axes are made on the substrate 1. Each axis of rotation passes through a distinct hinge. The moveable part 4 is covered with a high-reflectivity layer.
FIG. 1b represents a highly diagrammatic cross-sectional view of the different elements forming this type of micro-mirror (section along the axis of the hinge 5). In addition, in this Figure the different control electrodes 7, 8, 9 and 10 of the micro-mirror are represented. The opposing electrodes 7 and 8 make it possible to turn the moveable part 3 about the axis 5, which the opposing electrodes 9 and 10 make it possible to turn the moveable part about the axis 6.
The manufacturing steps comprise, starting with a mechanical substrate, a sequence of deposits and etchings of suitable material enabling the realization of the different elements of the micro-mirror or micro-mirrors (control electrodes, moveable parts, hinges, etc.) and comprise the use of one or a plurality of sacrificial layers, removal of which makes it possible to liberate the moveable part(s).
There are many technological alternatives for obtaining such devices. In this respect, the references cited at the end of the description can be consulted.
Although in the detail of the structures and the sequences of technological steps implemented use a wide diversity of approaches, the devices developed today have the following points in common:    the materials used for producing the moveable part or parts of the micro-mirrors are, in the majority of cases, amorphous or polycrystalline (polycrystalline silicon, aluminum, various metals, etc.) deposited using very classical techniques (vacuum evaporation, cathodic sputtering, vapor phase deposition, CVD, etc.)    the materials used for producing the sacrificial layers can be of different types (silica, various organic materials, etc.) but are always obtained by deposition techniques (CVD, rotary deposition, cathodic sputtering, etc.) that generally do not afford very precise control of the thicknesses utilized (typically several tens of nanometers for micron thicknesses) but that have the advantage of being very flexible to use.
The drawbacks of the prior art approaches are at several levels:    First of all, unsatisfactory precision in angular excursion (typically between 10−1 and 10−2) as the result of the use of sacrificial layers produced by deposition techniques that do not have very high degrees of thickness control.    For certain system architectures, in particular those used for optical routing purposes, all of these points are prejudicial and none of the manufacturing methods proposed in the prior art makes it possible to overcomes them correctly.    Moreover, poor mechanical properties of the amorphous or polycrystalline layers of the thin layers constituting the moveable part(s) that translates inter alia into a greater fragility and deformation after clearing, which perturbs the planeity of the surface.
This point is particularly important in the case of high surface micro-mirrors (of the order of a square millimeter or a fraction of a square millimeter) which must carry out an image function demanding excellent quality of optical wave surface.